From the discovery of superconductivity in 1911 to the recent past, essentially all known superconducting materials were elemental metals (e.g., Hg, the first known superconductor) or metal alloys (e.g., Nb.sub.3 Ge, probably the material with the highest transition temperature T.sub.c known prior to 1986).
Recently, superconductivity was discovered in a new class of materials. See, for instance, B. Batlogg, Physica, Vol. 126, 275 (1984), which reviews the properties of superconductivity in barium bismuth lead oxide, and J. G. Bednorz and K. A. Muller, Zeitschr. f. Physik B-Condensed Matter, Vol. 64, 189 (1986), which reports superconductivity in lanthanum barium copper oxide.
Especially the latter report stimulated worldwide research activity, which very quickly resulted in further significant progress. The progress has resulted, inter alia, to date in the discovery the compositions in the Y-Ba-Cu-O system can have superconductive transition temperatures T.sub.c above 77 K., the boiling temperature of liquid N.sub.2 (M. K. Wu et al, Phys. Rev. Letters, Vol. 58, Mar. 2, 1987, page 908; and P. H. Hor, ibid, page 911). Furthermore, it has resulted in the identification of the material phase that is responsible for the observed high temperature superconductivity, and in the discovery of compositions and processing techniques that result in the formation of bulk samples of material that can be substantially single phase material and can have T.sub.c above 90 K. (see the U.S. patent application Ser. No. 024,046, entitled "Devices and Systems Based on Novel Superconducting Material," filed by B. J. Batlogg, R. J. Cava and R. B. van Dover on Mar. 10, 1987, co-assigned with this and incorporated herein by reference, which is a continuation-in-part of an application filed by the same applicants on Mar. 3, 1987, which in turn is a continuation-in-part of application Ser. No. 001,682, filed by the same applicants on Jan. 9, 1987).
The excitement in the scientific and technical community that was created by the recent advances in superconductivity is at least in part due to the potentially immense technological impact of the availability of materials that are superconducting at temperatures that do not require refrigeration with expensive liquid He. Liquid nitrogen is generally considered to be the most convenient cryogenic refrigerant. Attainment of superconductivity at liquid nitrogen temperature was thus a long-sought goal which for a long time appeared almost unreachable.
Although this goal has now been attained, there still exists at least one barrier that has to be overcome before the new oxidic high T.sub.c superconductive materials can be utilized in many technological applications. In particular, techniques for forming superconductive bodies of technologically significant shape have to be developed.
The superconductive oxide material is readily produced in powder form, and has been processed by ceramic techniques into various shapes such as pellets, discs, and tori. A recently filed U.S. patent application Ser. No. 025,913, entitled "Apparatus Comprising a Cermaic Superconductive Body, and Method for Producing Such a Body", filed Mar. 16, 1987 by E. M. Gyorgy and D. W. Johnson, Jr., incorporated herein by reference, discloses techniques for making ceramic superconductive bodies having at least one relatively small dimension (5 .mu.m-1 mm). Such filamentary and sheet-like bodies include thin rods, filaments, tapes, and sheets, which can be incorporated into a variety of apparatus such as Bitter magnets, transmission lines, rotating machinery, maglev vehicles, and fusion devices.
Perhaps the economically most significant application of prior art metallic superconductors (e.g., Nb.sub.3 Sn) is in the form of magnet wires. Magnets incorporating such wires can be found in many scientific laboratories and, inter alia, are to be used in the proposed giant particle accelerator, the so-called "Superconducting Supercollider". Prior art superconductive wires universally have a composite structure, with one or more superconductive filaments embedded in normal metal, typically copper. The normal (i.e., nonsuperconductive.) metal, typically copper. The normal metal serves several critical functions in such wires, among them provision of a by-pass electrical conduction path, provision of thermal cnductive means in the event of local flux motion, and enhancement of the mechanical strength of the wire.
For an overview of some potential applications of superconductors see, for instance, B. B. Schwartz and S. Foner, editors, Superconductor Applications: SQUIDS and Machines, Plenum Press 1977; S. Foner and B. B. Schwartz, editors, Superconductor Material Science, Metallurgy, Fabrications, and Applications, Plenum Press 1981. Among the applications are power transmission lines, rotating machinery, and superconductive magnets for e.g., fusion generators, MHD generators, particle accelerators, levitated vehicles, magnetic separation, and energy storage. The prior art has considered these actual and potential applications in terms of the prior art (non-oxidic) superconductors. It is expected that many of the above and other applications of superconductivity would materially benefit it high T.sub.c superconductive wire could be used instead of the previously considered relatively low T.sub.c wire. We are disclosing herein techniques for producing such wire, as well as other bodies such as tape.